fellow_cache: Reduce stack usage in fellow_cache_obj_iter()

The fellow_e00029.vtc canary fell over on Ubuntu 20.04 with kernel 5.15

src/fellow_cache.c

@@ -3962,10 +3962,10 @@ fellow_cache_obj_iter(struct fellow_cache *fc, struct fellow_cache_obj *fco,
 	int ret2;
 
 	// 56 bytes per i_reqalloc + 176 bytes per reqs
-	// 56 * 8 + 2 * 176 = 800
+	// 56 * 7 + 2 * 176 = 800
 	struct buddy_reqs reqs[2] = {
 		BUDDY_REQS_LIT(fc->membuddy, 3),
-		BUDDY_REQS_LIT(fc->membuddy, 5)
+		BUDDY_REQS_LIT(fc->membuddy, 4)
 	};
 	unsigned newreqs = 0;